An example solution to improve the fuel economy of an internal combustion engine is a technology of setting a compression ratio to be high.
When the compression ratio is set to be high, however, there is a disadvantage that is likely to cause abnormal combustion, such as a knocking, or a pre-ignition before ignition.
In order to address such a disadvantage, a technology is known which delays the closing timing of an intake valve using a variable intake-valve mechanism upon detection of a knocking or detection of an ion current flowing through via a spark plug, i.e., retarding a so-called intake Variable Valve Timing (VVT), so that abnormal combustion can be avoided (see, for example, Patent Document 1).
According to this technology, however, in the case of an internal combustion engine especially under a severe running condition (e.g., a compression ratio is especially high, the interference in an exhaust process is large, or the like) and in an environment in which a water temperature and an intake temperature are both high (i.e., a heat-damage environment), it is difficult to suppress abnormal combustion only through the intake VVT retardation.
To address such a difficulty, there is a technology for cutting off a fuel supply to a cylinder at which the abnormal combustion has occurred to lower the temperature inside such a cylinder or to scavenge the interior thereof, thereby suppressing the abnormal combustion.
For example, in a technology disclosed in Patent Document 2, the fuel supply is cut off when any knocking is still detected even if the ignition timing is retarded to the retarded limit timing, so as to cool the interior of a cylinder.
Moreover, in a technology disclosed in Patent Document 3, the pressure inside a cylinder during a compression cycle is detected for cutting off the fuel supply to a cylinder that has caused a pre-ignition.